Precise Control Of The Relative Phase In A Two-color Laser Field By Mach-Zehnder Interferometer

The ultra-short laser pulse provides a powerful and efficient tool for studying ultrafast electron dynamics of atoms and molecules in strong laser fields.Recent years,there are many interesting phenomena such as above threshold ionization(ATI),non-sequential double ionization(NSDI),and high harmonic generation(HHG)have been explored.Those processes all result from the interaction between strong laser fields and atoms.As a tool to study the atomic and molecular dynamics in strong laser fields,the two-color laser field becomes a hot topic in the strong field atomic and molecular physics.Generally,a two-color laser field consists of a fundamental frequency light(?)and its second harmonic light(2?).In this field,the control precision of the relative phase between the two-color components has a crucial influence on the experimental results,which requires high stability for the optical paths in the experiment.The Mach-Zehnder interferometer allows one to change the parameter of the laser pulse on the two arms independently so that it becomes a common optical path in the experiments using two-color laser fields.However,due to the external disturbance in the laboratory,such as vibration,temperature changes and other factors,the two arms of the interferometer are disturbed variously.This can lead to additional difference in optical path and has a very significant impact on the precise control of the relative phase.Therefore,the stability of the Mach-Zehnder interferometer is very important for the precise control of the relative phase in the two-color laser field.In order to solve this problem,in this thesis we developed a scheme to stabilize the Mach-Zehnder interferometer based on active anti-vibration technology.In this scheme,a conventional Mach-Zehnder optical interferometers was set up.A 532 nm continuous wave(CW)propagated through both arms of the interferometer respectively.The interference fringes were recorded by an industrial camera in real time and the phase was extracted by Fast Fourier Transform(FFT).The phase difference between the interference structure at specific instant and the first one was taken as the error signal,and the PID(Proportion Integration Differentiation)algorithm converted the phase error signal into a voltage output signal.Finally,we applied the voltage to the PZT to compensate the additional optical path difference.In addition,the phase-stepping function was also set to control the relative phase.In the experiment,the influence of environmental disturbance on the Mach-Zehnder interferometer was studied,and the results showed that the phase drift of interference fringes is as high as dozens of radian in 3 hours.Under the same experimental condition,the stabilization scheme solved the interference fringe drift well and the fringe was stabilized to be near RMS=0.08 rad.Later,a two-color laser field light path is built using the Mach-Zehnder interferometer,the stabilization scheme were applied to study the phase dependence of the Ar electronic momentum distribution in the two-color laser field.In this experiment,the relative phase is precisely controlled by the stabilization scheme of Mach-Zehnder interferometer.The stabilization scheme of the Mach-Zehnder interferometer and the development of phase-stepping function allowed us to precisely control the relative phase of the two-color field,and this provided a basis for the study of the atoms and molecules with high temporal precision using the strong two-color laser field.